The L-α-Lysophosphatidylinositol/G Protein-Coupled Receptor 55 System Induces the Development of Nonalcoholic Steatosis and Steatohepatitis

Deletion of platelet-derived growth factor receptor β suppresses tumorigenesis in metabolic dysfunction-associated steatohepatitis (MASH) mice with diabetes

The platelet-derived growth factor (PDGF) family contributes to the progression of steatohepatitis; however, changes in and the characteristics of isoform-specific expression remain unclear. Since diabetes is a major driver of metabolic dysfunction-associated steatohepatitis (MASH), we characterized the mouse model of diabetic MASH (dMASH) by focusing on PDGF signaling. Pdgfa-d expression was markedly higher in hepatic stellate cells among flow-sorted cells in control mice and also increased in dMASH. In contrast, a reanalysis of human single-cell RNA-Seq data showed the distinct distribution of each PDGF isoform with disease progression. Furthermore, inflammation and fibrosis in the liver were less severe in diabetic MASH using tamoxifen-induced PDGF receptor β (PDGFRβ)-deficient mice (KO) than in control dMASH using floxed mice (FL) at 12 weeks old. Despite the absence of tumors, the expression of tumor-related genes was lower in KO than in FL. Tumorigenesis was significantly lower in 20-week-old KO. An Ingenuity Pathway Analysis of differentially expressed miRNA between FL and KO identified functional networks associated with hepatotoxicity and cancer. Therefore, PDGFRβ signals play important roles in the progression of steatohepatitis and tumorigenesis in MASH, with the modulation of miRNA expression posited as a potential underlying mechanism.

Global deletion of G protein-coupled receptor 55 impairs glucose homeostasis during obesity by reducing insulin secretion and β-cell turnover

AIM

To investigate the effect of G protein-coupled receptor 55 (GPR55) deletion on glucose homeostasis and islet function following diet-induced obesity.

METHODS

GPR55-/- and wild-type (WT) mice were fed ad libitum either standard chow (SC) or a high-fat diet (HFD) for 20 weeks. Glucose and insulin tolerance tests were performed at 9/10 and 19/20 weeks of dietary intervention. Insulin secretion in vivo and dynamic insulin secretion following perifusion of isolated islets were also determined, as were islet caspase-3/7 activities and β-cell 5-bromo-20-deoxyuridine (BrdU) incorporation.

RESULTS

GPR55-/- mice fed a HFD were more susceptible to diet-induced obesity and were more glucose intolerant and insulin resistant than WT mice maintained on a HFD. Islets isolated from HFD-fed GPR55-/- mice showed impaired glucose- and pcacahorbol 12-myristate 13-acetate-stimulated insulin secretion, and they also displayed increased cytokine-induced apoptosis. While there was a 5.6 ± 1.6-fold increase in β-cell BrdU incorporation in the pancreases of WT mice fed a HFD, this compensatory increase in β-cell proliferation in response to the HFD was attenuated in GPR55-/- mice.

CONCLUSIONS

Under conditions of diet-induced obesity, GPR55-/- mice show impaired glucose handling, which is associated with reduced insulin secretory capacity, increased islet cell apoptosis and insufficient compensatory increases in β-cell proliferation. These observations support that GPR55 plays an important role in positively regulating islet function.

Discovery of Novel Peptide Antagonists Targeting GPR55 for Liver Inflammation and Fibrosis

Liver fibrosis is a condition characterized by aberrant proliferation of connective tissue in the liver resulting from diverse etiological factors. G protein-coupled receptor GPR55 has recently been identified as a regulator of liver diseases. Herein, we report the discovery of a cyclic peptide P1-1 that antagonizes GPR55 and suppresses collagen secretion in hepatic stellate cells. The alanine scanning and docking study was carried out to predict the binding mode and allowed for further structural optimization of peptide antagonists for GPR55. The subsequent in vivo study demonstrated that P1-1 ameliorates CCl4-induce and MCD-diet-induce acute liver inflammation and fibrosis. Further study indicates that P1-1 reduces reactive oxygen species (ROS) production, attenuates ER stress, and inhibits mitochondria-associated hepatocyte apoptosis. In this work, we provided the first successful example of antagonizing GPR55 for liver inflammation and fibrosis, which validates GPR55 as a promising target for the treatment of liver fibrosis and affords a high-potent GPR55 antagonist P1-1 as a potential therapeutic candidate.

GPR55 Antagonist CID16020046 Attenuates Obesity-Induced Airway Inflammation by Suppressing Chronic Low-Grade Inflammation in the Lungs

GPR55 is a receptor for lysophosphatidylinositols (LPIs) in digestive metabolites. Overnutrition leads to obesity, insulin resistance, and increased LPI levels in the plasma. The involvement of LPIs and GPR55 in adiposity, hepatic steatosis, and atherosclerosis has been previously elucidated. However, the therapeutic efficacy of GPR55 antagonists against obesity-induced airway inflammation has not been studied. The present study investigated whether CID16020046, a selective antagonist of GPR55, could modulate obesity-induced airway inflammation caused by a high-fat diet (HFD) in C57BL/6 mice. Administration of CID16020046 (1 mg/kg) inhibits HFD-induced adiposity and glucose intolerance. Analysis of immune cells in BALF showed that CID16020046 inhibited HFD-induced increase in immune cell infiltration. Histological analysis revealed the HFD induced hypersecretion of mucus and extensive fibrosis in the lungs. CID16020046 inhibited these HFD-induced pathological features. qRT-PCR revealed the HFD-induced increase in the expression of Ifn-γ, Tnf-α, Il-6, Il-13, Il-17A, Il-1β, Nlrp3, and Mpo mRNAs in the lungs. CID16020046 inhibited the HFD-induced increases in these genes. The expression levels of adipokines were regulated by the HFD and CID16020046. AdipoQ in the lungs and gonadal white adipose tissue was decreased by the HFD and reversed by CID16020046. In contrast, Lep was increased by the HFD and suppressed by CID16020046. The findings suggest the potential application of the GPR55 antagonist CID16020046 in obesity-induced airway inflammation.

Inhibition of hepatic p63 ameliorates steatohepatitis with fibrosis in mice

OBJECTIVE

p63 is a transcription factor involved in multiple biological functions. In the liver, the TAp63 isoform induces lipid accumulation in hepatocytes. However, the role of liver TAp63 in the progression of metabolic dysfunction-associated steatohepatitis (MASH) with fibrosis is unknown.

METHODS

We evaluated the hepatic p63 levels in different mouse models of steatohepatitis with fibrosis induced by diet. Next, we used virogenetic approaches to manipulate the expression of TAp63 in adult mice under diet-induced steatohepatitis with fibrosis and characterized the disease condition. Finally, we performed proteomics analysis in mice with overexpression and knockdown of hepatic TAp63.

RESULTS

Levels of TAp63, but not of ΔN isoform, are increased in the liver of mice with diet-induced steatohepatitis with fibrosis. Both preventive and interventional strategies for the knockdown of hepatic TAp63 significantly ameliorated diet-induced steatohepatitis with fibrosis in mice fed a methionine- and choline-deficient diet (MCDD) and choline deficient and high fat diet (CDHFD). The overexpression of hepatic TAp63 in mice aggravated the liver condition in mice fed a CDHFD. Proteomic analysis in the liver of these mice revealed alteration in multiple proteins and pathways, such as oxidative phosphorylation, antioxidant activity, peroxisome function and LDL clearance.

CONCLUSIONS

These results indicate that liver TAp63 plays a critical role in the progression of diet-induced steatohepatitis with fibrosis, and its inhibition ameliorates the disease.

GPCRs involved in metabolic diseases: pharmacotherapeutic development updates

G protein-coupled receptors (GPCRs) are expressed in a variety of cell types and tissues, and activation of GPCRs is involved in enormous metabolic pathways, including nutrient synthesis, transportation, storage or insulin sensitivity, etc. This review intends to summarize the regulation of metabolic homeostasis and mechanisms by a series of GPCRs, such as GPR91, GPR55, GPR119, GPR109a, GPR142, GPR40, GPR41, GPR43 and GPR120. With deep understanding of GPCR's structure and signaling pathways, it is attempting to uncover the role of GPCRs in major metabolic diseases, including metabolic syndrome, diabetes, dyslipidemia and nonalcoholic steatohepatitis, for which the global prevalence has risen during last two decades. An extensive list of agonists and antagonists with their chemical structures in a nature of small molecular compounds for above-mentioned GPCRs is provided as pharmacologic candidates, and their preliminary data of preclinical studies are discussed. Moreover, their beneficial effects in correcting abnormalities of metabolic syndrome, diabetes and dyslipidemia are summarized when clinical trials have been undertaken. Thus, accumulating data suggest that these agonists or antagonists might become as new pharmacotherapeutic candidates for the treatment of metabolic diseases.

Modulation of neuroinflammation and oxidative stress by targeting GPR55 - new approaches in the treatment of psychiatric disorders

Pharmacological treatment of psychiatric disorders remains challenging in clinical, pharmacological, and scientific practice. Even if many different substances are established for treating different psychiatric conditions, subgroups of patients show only small or no response to the treatment. The neuroinflammatory hypothesis of the genesis of psychiatric disorders might explain underlying mechanisms in these non-responders. For that reason, recent research focus on neuroinflammatory processes and oxidative stress as possible causes of psychiatric disorders. G-protein coupled receptors (GPCRs) form the biggest superfamily of membrane-bound receptors and are already well known as pharmacological targets in various diseases. The G-protein coupled receptor 55 (GPR55), a receptor considered part of the endocannabinoid system, reveals promising modulation of neuroinflammatory and oxidative processes. Different agonists and antagonists reduce pro-inflammatory cytokine release, enhance the synthesis of anti-inflammatory mediators, and protect cells from oxidative damage. For this reason, GPR55 ligands might be promising compounds in treating subgroups of patients suffering from psychiatric disorders related to neuroinflammation or oxidative stress. New approaches in drug design might lead to new compounds targeting different pathomechanisms of those disorders in just one molecule.

Mitochondrial antiviral signaling protein enhances MASLD progression through the ERK/TNFα/NFκβ pathway

BACKGROUND AND AIMS

Mitochondrial antiviral signaling protein (MAVS) is a critical regulator that activates the host's innate immunity against RNA viruses, and its signaling pathway has been linked to the secretion of proinflammatory cytokines. However, the actions of MAVS on inflammatory pathways during the development of metabolic dysfunction-associated steatotic liver disease (MASLD) have been little studied.

APPROACH AND RESULTS

Liver proteomic analysis of mice with genetically manipulated hepatic p63, a transcription factor that induces liver steatosis, revealed MAVS as a target downstream of p63. MAVS was thus further evaluated in liver samples from patients and in animal models with MASLD. Genetic inhibition of MAVS was performed in hepatocyte cell lines, primary hepatocytes, spheroids, and mice. MAVS expression is induced in the liver of both animal models and people with MASLD as compared with those without liver disease. Using genetic knockdown of MAVS in adult mice ameliorates diet-induced MASLD. In vitro, silencing MAVS blunts oleic and palmitic acid-induced lipid content, while its overexpression increases the lipid load in hepatocytes. Inhibiting hepatic MAVS reduces circulating levels of the proinflammatory cytokine TNFα and the hepatic expression of both TNFα and NFκβ. Moreover, the inhibition of ERK abolished the activation of TNFα induced by MAVS. The posttranslational modification O -GlcNAcylation of MAVS is required to activate inflammation and to promote the high lipid content in hepatocytes.

CONCLUSIONS

MAVS is involved in the development of steatosis, and its inhibition in previously damaged hepatocytes can ameliorate MASLD.

Endocannabinoid-related molecules predict the metabolic efficacy of GLP-1 receptor agonism in humans with obesity

OBJECTIVE

N-acylethanolamines (NAEs) include endocannabinoid (EC) and EC-related molecules that impact the anti-obesity and anti-diabetic efficacy of glucagon-like peptide-1 receptor agonists (GLP-1RA) in animal studies. However, the clinical relevance of these findings remains to be determined. Here, we tested whether GLP-1RA treatment affects circulating NAE levels and whether NAEs may predict the efficacy of GLP-1RA treatment in humans with obesity undergoing weight loss maintenance.

MATERIALS AND METHODS

We profiled plasma levels of NAEs in participants with obesity undergoing weight loss maintenance with (n = 23)/or without (n = 20) treatment with the GLP-1RA liraglutide. NAE levels were measured at three different time points: before the start of the study, at the end of the diet-induced weight loss, and after 52-weeks treatment. Linear regression analyses were used to investigate whether pharmacological responses could be predicted by NAEs levels.

RESULTS

Liraglutide treatment reduced plasma concentrations of the NAE and oleoyl-ethanolamide (OEA), without altering arachidonoyl-ethanolamide (AEA) levels and palmitoyl-ethanolamide (PEA) levels. High pre-treatment levels of OEA were predictive of superior compound-mediated effects on fasting insulin and triglyceride levels. High pre-treatment PEA and AEA levels were also predictive of superior Liraglutide-mediated effects on triglyceride levels.

CONCLUSIONS

Our data suggests that specific NAEs such as OEA and AEA are promising biomarkers of GLP-1RA metabolic efficacy in humans with obesity during weight loss maintenance. Plasma profiling of EC-related molecules may be a promising strategy to tailor GLP-1R-based therapies to individual needs in obesity and diabetes management.

p63 controls metabolic activation of hepatic stellate cells and fibrosis via an HER2-ACC1 pathway

The p63 protein has pleiotropic functions and, in the liver, participates in the progression of nonalcoholic fatty liver disease (NAFLD). However, its functions in hepatic stellate cells (HSCs) have not yet been explored. TAp63 is induced in HSCs from animal models and patients with liver fibrosis and its levels positively correlate with NAFLD activity score and fibrosis stage. In mice, genetic depletion of TAp63 in HSCs reduces the diet-induced liver fibrosis. In vitro silencing of p63 blunts TGF-β1-induced HSCs activation by reducing mitochondrial respiration and glycolysis, as well as decreasing acetyl CoA carboxylase 1 (ACC1). Ectopic expression of TAp63 induces the activation of HSCs and increases the expression and activity of ACC1 by promoting the transcriptional activity of HER2. Genetic inhibition of both HER2 and ACC1 blunt TAp63-induced activation of HSCs. Thus, TAp63 induces HSC activation by stimulating the HER2-ACC1 axis and participates in the development of liver fibrosis.

The Role of Cannabidiol in Liver Disease: A Systemic Review

Cannabidiol (CBD), a non-psychoactive phytocannabinoid abundant in Cannabis sativa, has gained considerable attention for its anti-inflammatory, antioxidant, analgesic, and neuroprotective properties. It exhibits the potential to prevent or slow the progression of various diseases, ranging from malignant tumors and viral infections to neurodegenerative disorders and ischemic diseases. Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease, and viral hepatitis stand as prominent causes of morbidity and mortality in chronic liver diseases globally. The literature has substantiated CBD's potential therapeutic effects across diverse liver diseases in in vivo and in vitro models. However, the precise mechanism of action remains elusive, and an absence of evidence hinders its translation into clinical practice. This comprehensive review emphasizes the wealth of data linking CBD to liver diseases. Importantly, we delve into a detailed discussion of the receptors through which CBD might exert its effects, including cannabinoid receptors, CB1 and CB2, peroxisome proliferator-activated receptors (PPARs), G protein-coupled receptor 55 (GPR55), transient receptor potential channels (TRPs), and their intricate connections with liver diseases. In conclusion, we address new questions that warrant further investigation in this evolving field.

The Interaction of the Endocannabinoid Anandamide and Paracannabinoid Lysophosphatidylinositol during Cell Death Induction in Human Breast Cancer Cells

Endocannabinoid anandamide (AEA) and paracannabinoid lysophosphatidylinositol (LPI) play a significant role in cancer cell proliferation regulation. While anandamide inhibits the proliferation of cancer cells, LPI is known as a cancer stimulant. Despite the known endocannabinoid receptor crosstalk and simultaneous presence in the cancer microenvironment of both molecules, their combined activity has never been studied. We evaluated the effect of LPI on the AEA activity in six human breast cancer cell lines of different carcinogenicity (MCF-10A, MCF-7, BT-474, BT-20, SK-BR-3, MDA-MB-231) using resazurin and LDH tests after a 72 h incubation. AEA exerted both anti-proliferative and cytotoxic activity with EC50 in the range from 31 to 80 µM. LPI did not significantly affect the cell viability. Depending on the cell line, the response to the LPI-AEA combination varied from a decrease in AEA cytotoxicity to an increase in it. Based on the inhibitor analysis of the endocannabinoid receptor panel, we showed that for the former effect, an active GPR18 receptor was required and for the latter, an active CB2 receptor. The data obtained for the first time are important for the understanding the manner by which endocannabinoid receptor ligands acting simultaneously can modulate cancer growth at different stages.

Bioactive signalling lipids as drivers of chronic liver diseases

Lipids are important in multiple cellular functions, with most having structural or energy storage roles. However, a small fraction of lipids exert bioactive roles through binding to G protein-coupled receptors and induce a plethora of processes including cell proliferation, differentiation, growth, migration, apoptosis, senescence and survival. Bioactive signalling lipids are potent modulators of metabolism and energy homeostasis, inflammation, tissue repair and malignant transformation. All these events are involved in the initiation and progression of chronic liver diseases. In this review, we focus specifically on the roles of bioactive lipids derived from phospholipids (lyso-phospholipids) and poly-unsaturated fatty acids (eicosanoids, pro-resolving lipid mediators and endocannabinoids) in prevalent chronic liver diseases (alcohol-associated liver disease, non-alcoholic fatty liver disease, viral hepatitis and hepatocellular carcinoma). We discuss the balance between pathogenic and beneficial bioactive lipids as well as potential therapeutic targets related to the agonism or antagonism of their receptors.

MBOAT7 in liver and extrahepatic diseases

MBOAT7 is a protein anchored to endomembranes by several transmembrane domains. It has a catalytic dyad involved in remodelling of phosphatidylinositol with polyunsaturated fatty acids. Genetic variants in the MBOAT7 gene have been associated with the entire spectrum of non-alcoholic fatty liver (NAFLD), recently redefined as metabolic dysfunction-associated fatty liver disease (MAFLD) and, lately, steatotic liver disease (SLD), and to an increasing number of extrahepatic conditions. In this review, we will (a) elucidate the molecular mechanisms by which MBOAT7 loss-of-function predisposes to MAFLD and neurodevelopmental disorders and (b) discuss the growing number of genetic studies linking MBOAT7 to hepatic and extrahepatic diseases. MBOAT7 complete loss of function causes severe changes in brain development resulting in several neurological manifestations. Lower MBOAT7 hepatic expression at both the mRNA and protein levels, due to missense nucleotide polymorphisms (SNPs) in the locus containing the MBOAT7 gene, affects specifically metabolic and viral diseases in the liver from simple steatosis to hepatocellular carcinoma, and potentially COVID-19 disease. This body of evidence shows that phosphatidylinositol remodelling is a key factor for human health.

The effect of N-arachidonoylethanolamide administration on energy and fat metabolism of early lactating dairy cows

The aim of the study was to investigate the effect of N-arachidonoylethanolamide (AEA), an endocannabinoid with orexigenic characteristics, on plasma endocannabinoid concentrations, feed intake, energy balance, lipomobilisation, and hepatic lipid metabolism of early-lactating dairy cows. The experiment involved 10 pairs of Holstein half-sibling cows (end of 2nd-3rd pregnancy). Half-sibs of each pair were randomly assigned to either AEA (n = 10) or control (CON) group (n = 10). From day 1 to 30 postpartum, the AEA group received 5 intraperitoneal injections per week of 3 µg/kg body weight AEA and the CON group 0.9% NaCl. In week 1-3 postpartum, AEA administration had no effect on dry matter intake, body weight, or lipomobilisation, but increased plasma triglyceride concentration on d 21 p.p. and mRNA abundances of genes related to hepatic triglyceride synthesis. In week 4 postpartum, the AEA group showed reduced feed intake and whole-body carbohydrate oxidation, but increased whole-body fat oxidation and hepatic lipid accumulation, likely as a result of a counter-regulatory leptin increase. In conclusion, the present study shows a tissue-specific AEA insensitivity and may point to a leptin-controlled regulation of the ECS in early-lactation.

GPCRs and fibroblast heterogeneity in fibroblast-associated diseases

G protein-coupled receptors (GPCRs) are the largest and most diverse class of signaling receptors. GPCRs regulate many functions in the human body and have earned the title of "most targeted receptors". About one-third of the commercially available drugs for various diseases target the GPCRs. Fibroblasts lay the architectural skeleton of the body, and play a key role in supporting the growth, maintenance, and repair of almost all tissues by responding to the cellular cues via diverse and intricate GPCR signaling pathways. This review discusses the dynamic architecture of the GPCRs and their intertwined signaling in pathological conditions such as idiopathic pulmonary fibrosis, cardiac fibrosis, pancreatic fibrosis, hepatic fibrosis, and cancer as opposed to the GPCR signaling of fibroblasts in physiological conditions. Understanding the dynamics of GPCR signaling in fibroblasts with disease progression can help in the recognition of the complex interplay of different GPCR subtypes in fibroblast-mediated diseases. This review highlights the importance of designing and adaptation of next-generation strategies such as GPCR-omics, focused target identification, polypharmacology, and effective personalized medicine approaches to achieve better therapeutic outcomes for fibrosis and fibrosis associated malignancies.

Warm Ischemia Induces Spatiotemporal Changes in Lysophosphatidylinositol That Affect Post-Reperfusion Injury in Normal and Steatotic Rat Livers

Warm ischemia-reperfusion injury is a prognostic factor for hepatectomy and liver transplantation. However, its underlying molecular mechanisms are unknown. This study aimed to elucidate these mechanisms and identify the predictive markers of post-reperfusion injury. Rats with normal livers were subjected to 70% hepatic warm ischemia for 15, 30, or 90 min, while those with steatotic livers were subjected to 70% hepatic warm ischemia for only 30 min. The liver and blood were sampled at the end of ischemia and 1, 6, and 24 h after reperfusion. The serum alanine aminotransferase (ALT) activity, Suzuki injury scores, and lipid peroxidation (LPO) products were evaluated. The ALT activity and Suzuki scores increased with ischemic duration and peaked at 1 and 6 h after reperfusion, respectively. Steatotic livers subjected to 30 min ischemia and normal livers subjected to 90 min ischemia showed comparable injury. A similar trend was observed for LPO products. Imaging mass spectrometry of normal livers revealed an increase in lysophosphatidylinositol (LPI (18:0)) and a concomitant decrease in phosphatidylinositol (PI (18:0/20:4)) in Zone 1 (central venous region) with increasing ischemic duration; they returned to their basal values after reperfusion. Similar changes were observed in steatotic livers. Hepatic warm ischemia time-dependent acceleration of PI (18:0/20:4) to LPI (18:0) conversion occurs initially in Zone 1 and is more pronounced in fatty livers. Thus, the LPI (18:0)/PI (18:0/20:4) ratio is a potential predictor of post-reperfusion injury.

Saturated fatty acids increase LPI to reduce FUNDC1 dimerization and stability and mitochondrial function

Ectopic lipid deposition and mitochondrial dysfunction are common etiologies of obesity and metabolic disorders. Excessive dietary uptake of saturated fatty acids (SFAs) causes mitochondrial dysfunction and metabolic disorders, while unsaturated fatty acids (UFAs) counterbalance these detrimental effects. It remains elusive how SFAs and UFAs differentially signal toward mitochondria for mitochondrial performance. We report here that saturated dietary fatty acids such as palmitic acid (PA), but not unsaturated oleic acid (OA), increase lysophosphatidylinositol (LPI) production to impact on the stability of the mitophagy receptor FUNDC1 and on mitochondrial quality. Mechanistically, PA shifts FUNDC1 from dimer to monomer via enhanced production of LPI. Monomeric FUNDC1 shows increased acetylation at K104 due to dissociation of HDAC3 and increased interaction with Tip60. Acetylated FUNDC1 can be further ubiquitinated by MARCH5 for proteasomal degradation. Conversely, OA antagonizes PA-induced accumulation of LPI, and FUNDC1 monomerization and degradation. A fructose-, palmitate-, and cholesterol-enriched (FPC) diet also affects FUNDC1 dimerization and promotes its degradation in a non-alcoholic steatohepatitis (NASH) mouse model. We thus uncover a signaling pathway that orchestrates lipid metabolism with mitochondrial quality.

Associations of altered hepatic gene expression in American lifestyle-induced obesity syndrome diet-fed mice with metabolic changes during NAFLD development and progression

Non-alcoholic fatty liver disease (NAFLD) pathogenesis remains poorly understood due to the complex metabolic and inflammatory changes in the liver. This study aimed to elucidate hepatic events related to inflammation and lipid metabolism and their linkage with metabolic alterations during NAFLD in American lifestyle-induced obesity syndrome (ALIOS) diet-fed mice. Forty-eight C57BL/6J male mice were fed with ALIOS diet (n=24) or control chow diet (n=24) for 8, 12, and 16 weeks. At the end of each timepoint, eight mice were sacrificed where plasma and liver were collected. Hepatic fat accumulation was followed using magnetic resonance imaging and confirmed with histology. Further, targeted gene expression and non-targeted metabolomics analysis were conducted. Our results showed higher hepatic steatosis, body weight, energy consumption, and liver mass in ALIOS diet-fed mice compared to control mice. ALIOS diet altered expression of genes related to inflammation (Tnfa and IL-6) and lipid metabolism (Cd36, Fasn, Scd1, Cpt1a, and Ppara). Metabolomics analysis indicated decrease of lipids containing polyunsaturated fatty acids such as LPE(20:5) and LPC(20:5) with increase of other lipid species such as LPI(16:0) and LPC(16:2) and peptides such as alanyl-phenylalanine and glutamyl-arginine. We further observed novel correlations between different metabolites including sphingolipid, lysophospholipids, peptides, and bile acid with inflammation, lipid uptake and synthesis. Together with the reduction of antioxidant metabolites and gut microbiota-derived metabolites contribute to NAFLD development and progression. The combination of non-targeted metabolomics with gene expression in future studies can further identify key metabolic routes during NAFLD which could be the targets of potential novel therapeutics.

Hepatic Stellate Cells: Dictating Outcome in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a fast growing, chronic liver disease affecting ∼25% of the global population. Nonalcoholic fatty liver disease severity ranges from the less severe simple hepatic steatosis to the more advanced nonalcoholic steatohepatitis (NASH). The presence of NASH predisposes individuals to liver fibrosis, which can further progress to cirrhosis and hepatocellular carcinoma. This makes hepatic fibrosis an important indicator of clinical outcomes in patients with NASH. Hepatic stellate cell activation dictates fibrosis development during NASH. Here, we discuss recent advances in the analysis of the profibrogenic pathways and mediators of hepatic stellate cell activation and inactivation, which ultimately determine the course of disease in nonalcoholic fatty liver disease/NASH.

Plasma Metabolite Signatures in Male Carriers of Genetic Variants Associated with Non-Alcoholic Fatty Liver Disease

Both genetic and non-genetic factors are important in the pathophysiology of non-alcoholic fatty liver disease (NAFLD). The aim of our study was to identify novel metabolites and pathways associated with NAFLD by including both genetic and non-genetic factors in statistical analyses. We genotyped six genetic variants in the PNPLA3, TM6SF2, MBOAT7, GCKR, PPP1R3B, and HSD17B13 genes reported to be associated with NAFLD. Non-targeted metabolomic profiling was performed from plasma samples. We applied a previously validated fatty liver index to identify participants with NAFLD. First, we associated the six genetic variants with 1098 metabolites in 2 339 men without NAFLD to determine the effects of the genetic variants on metabolites, and then in 2 535 men with NAFLD to determine the joint effects of genetic variants and non-genetic factors on metabolites. We identified several novel metabolites and metabolic pathways, especially for PNPLA3, GCKR, and PPP1R38 variants relevant to the pathophysiology of NAFLD. Importantly, we showed that each genetic variant for NAFLD had a specific metabolite signature. The plasma metabolite signature was unique for each genetic variant, suggesting that several metabolites and different pathways are involved in the risk of NAFLD. The FLI index reliably identifies metabolites for NAFLD in large population-based studies.

Pathogenesis and treatment of non-alcoholic steatohepatitis and its fibrosis

The initial presentation of non-alcoholic steatohepatitis (NASH) is hepatic steatosis. The dysfunction of lipid metabolism within hepatocytes caused by genetic factors, diet, and insulin resistance causes lipid accumulation. Lipotoxicity, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum stress would further contribute to hepatocyte injury and death, leading to inflammation and immune dysfunction in the liver. During the healing process, the accumulation of an excessive amount of fibrosis might occur while healing. During the development of NASH and liver fibrosis, the gut-liver axis, adipose-liver axis, and renin-angiotensin system (RAS) may be dysregulated and impaired. Translocation of bacteria or its end-products entering the liver could activate hepatocytes, Kupffer cells, and hepatic stellate cells, exacerbating hepatic steatosis, inflammation, and fibrosis. Bile acids regulate glucose and lipid metabolism through Farnesoid X receptors in the liver and intestine. Increased adipose tissue-derived non-esterified fatty acids would aggravate hepatic steatosis. Increased leptin also plays a role in hepatic fibrogenesis, and decreased adiponectin may contribute to hepatic insulin resistance. Moreover, dysregulation of peroxisome proliferator-activated receptors in the liver, adipose, and muscle tissues may impair lipid metabolism. In addition, the RAS may contribute to hepatic fatty acid metabolism, inflammation, and fibrosis. The treatment includes lifestyle modification, pharmacological therapy, and non-pharmacological therapy. Currently, weight reduction by lifestyle modification or surgery is the most effective therapy. However, vitamin E, pioglitazone, and obeticholic acid have also been suggested. In this review, we will introduce some new clinical trials and experimental therapies for the treatment of NASH and related fibrosis.

Thienopyrimidine Derivatives as GPR55 Receptor Antagonists: Insight into Structure-Activity Relationship

GPR55 is an orphan G-protein coupled receptor involved in various pathophysiological conditions. However, there are only a few noncannabinoid GPR55 ligands reported so far. The lack of potent and selective GPR55 ligands precludes a deep exploration of this receptor. The studies presented here focused on a thienopyrimidine scaffold based on the GPR55 antagonist ML192, previously discovered by high-throughput screening. The GPR55 activities of the new synthesized compounds were assessed using β-arrestin recruitment assays in Chinese hamster ovary cells overexpressing human GPR55. Some derivatives were identified as GPR55 antagonists with functional efficacy and selectivity versus CB1 and CB2 cannabinoid receptors.

GPR55 in B cells limits atherosclerosis development and regulates plasma cell maturation

Dissecting the pathways regulating the adaptive immune response in atherosclerosis is of particular therapeutic interest. Here we report that the lipid G-protein coupled receptor GPR55 is highly expressed by splenic plasma cells (PC), upregulated in mouse spleens during atherogenesis and human unstable or ruptured compared to stable plaques. Gpr55-deficient mice developed larger atherosclerotic plaques with increased necrotic core size compared to their corresponding controls. Lack of GPR55 hyperactivated B cells, disturbed PC maturation and resulted in immunoglobulin (Ig)G overproduction. B cell-specific Gpr55 depletion or adoptive transfer of Gpr55-deficient B cells was sufficient to promote plaque development and elevated IgG titers. In vitro, the endogenous GPR55 ligand lysophsophatidylinositol (LPI) enhanced PC proliferation, whereas GPR55 antagonism blocked PC maturation and increased their mitochondrial content. Collectively, these discoveries provide previously undefined evidence for GPR55 in B cells as a key modulator of the adaptive immune response in atherosclerosis.

Comprehensive molecular mechanisms and clinical therapy in nonalcoholic steatohepatitis: An overview and current perspectives

Our understanding of nonalcoholic steatohepatitis (NASH) pathophysiology continues to advance rapidly. Given the complexity of the pathogenesis of NASH, the field has moved from describing the single pathogenesis of NASH to deeply phenotyping with a description of the multi-mechanism and multi-target pathogenesis that includes glucose, lipid and cholesterol metabolism, fibrotic progression, inflammation, immune reaction and apoptosis. To make the picture more complex, the pathogenesis of NASH involves pathological connections between the liver and several organs such as the adipose, pancreas, kidney and gut. Numerous pharmacologic candidates have been tested in clinical trials and have generated some positive results. Importantly, PPAR as triglyceride synthesis inhibitor and FXR as bile acids synthesis inhibitor have displayed beneficial effects on candidates for lipid and cholesterol metabolism. Although the efficacy of these drugs has been affirmed, serious side effects hinder their further development. It is a particularly important task to carry out the in-depth long-term research. Additionally, drug combination increases response rate and reduces side effects of a single drug. Mastering the advantages and limitations of clinical candidate drugs and continuous improvement and innovation are necessary to formulate a new strategy for the future treatment of NASH.

Prolonged breastfeeding protects from obesity by hypothalamic action of hepatic FGF21

Early-life determinants are thought to be a major factor in the rapid increase of obesity. However, while maternal nutrition has been extensively studied, the effects of breastfeeding by the infant on the reprogramming of energy balance in childhood and throughout adulthood remain largely unknown. Here we show that delayed weaning in rat pups protects them against diet-induced obesity in adulthood, through enhanced brown adipose tissue thermogenesis and energy expenditure. In-depth metabolic phenotyping in this rat model as well as in transgenic mice reveals that the effects of prolonged suckling are mediated by increased hepatic fibroblast growth factor 21 (FGF21) production and tanycyte-controlled access to the hypothalamus in adulthood. Specifically, FGF21 activates GABA-containing neurons expressing dopamine receptor 2 in the lateral hypothalamic area and zona incerta. Prolonged breastfeeding thus constitutes a protective mechanism against obesity by affecting long-lasting physiological changes in liver-to-hypothalamus communication and hypothalamic metabolic regulation.

Membrane-bound O-acyltransferase 7 (MBOAT7)-driven phosphatidylinositol remodeling in advanced liver disease

Advanced liver diseases account for approximately 2 million deaths annually worldwide. Roughly, half of liver disease-associated deaths arise from complications of cirrhosis and the other half driven by viral hepatitis and hepatocellular carcinoma. Unfortunately, the development of therapeutic strategies to treat subjects with advanced liver disease has been hampered by a lack of mechanistic understanding of liver disease progression and a lack of human-relevant animal models. An important advance has been made within the past several years, as several genome-wide association studies have discovered that an SNP near the gene encoding membrane-bound O-acyltransferase 7 (MBOAT7) is associated with severe liver diseases. This common MBOAT7 variant (rs641738, C>T), which reduces MBOAT7 expression, confers increased susceptibility to nonalcoholic fatty liver disease, alcohol-associated liver disease, and liver fibrosis in patients chronically infected with viral hepatitis. Recent studies in mice also show that Mboat7 loss of function can promote hepatic steatosis, inflammation, and fibrosis, causally linking this phosphatidylinositol remodeling enzyme to liver health in both rodents and humans. Herein, we review recent insights into the mechanisms by which MBOAT7-driven phosphatidylinositol remodeling influences liver disease progression and discuss how rapid progress in this area could inform drug discovery moving forward.

Fibrogenic Pathways in Metabolic Dysfunction Associated Fatty Liver Disease (MAFLD)

The prevalence of nonalcoholic fatty liver disease (NAFLD), recently also re-defined as metabolic dysfunction associated fatty liver disease (MAFLD), is rapidly increasing, affecting ~25% of the world population. MALFD/NAFLD represents a spectrum of liver pathologies including the more benign hepatic steatosis and the more advanced non-alcoholic steatohepatitis (NASH). NASH is associated with enhanced risk for liver fibrosis and progression to cirrhosis and hepatocellular carcinoma. Hepatic stellate cells (HSC) activation underlies NASH-related fibrosis. Here, we discuss the profibrogenic pathways, which lead to HSC activation and fibrogenesis, with a particular focus on the intercellular hepatocyte–HSC and macrophage–HSC crosstalk.

GPR55 Antagonist CID16020046 Protects against Atherosclerosis Development in Mice by Inhibiting Monocyte Adhesion and Mac-1 Expression

GPR55 recognizes several lipid molecules such as lysophosphatidylinositol. GPR55 expression was reported in human monocytes. However, its role in monocyte adhesion and atherosclerosis development has not been studied. The role of GPR55 in monocyte adhesion and atherosclerosis development was investigated in human THP-1 monocytes and ApoE^-/- mice using O-1602 (a potent agonist of GPR55) and CID16020046 (a specific GPR55 antagonist). O-1602 treatment significantly increased monocyte adhesion to human umbilical vein endothelial cells, and the O-1602-induced adhesion was inhibited by treatment with CID16020046. O-1602 induced the expression of Mac-1 adhesion molecules, whereas CID16020046 inhibited this induction. Analysis of the promoter region of Mac-1 elucidated the binding sites of AP-1 and NF-κB between nucleotides -750 and -503 as GPR55 responsive elements. O-1602 induction of Mac-1 was found to be dependent on the signaling components of GPR55, that is, Gq protein, Ca²⁺, CaMKK, and PI3K. In Apo^-/- mice, administration of CID16020046 ameliorated high-fat diet-induced atherosclerosis development. These results suggest that high-fat diet-induced GPR55 activation leads to the adhesion of monocytes to endothelial cells via induction of Mac-1, and CID16020046 blockage of GPR55 could suppress monocyte adhesion to vascular endothelial cells through suppression of Mac-1 expression, leading to protection against the development of atherosclerosis.

Metabolomics and lipidomics in NAFLD: biomarkers and non-invasive diagnostic tests

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide and is often associated with aspects of metabolic syndrome. Despite its prevalence and the importance of early diagnosis, there is a lack of robustly validated biomarkers for diagnosis, prognosis and monitoring of disease progression in response to a given treatment. In this Review, we provide an overview of the contribution of metabolomics and lipidomics in clinical studies to identify biomarkers associated with NAFLD and nonalcoholic steatohepatitis (NASH). In addition, we highlight the key metabolic pathways in NAFLD and NASH that have been identified by metabolomics and lipidomics approaches and could potentially be used as biomarkers for non-invasive diagnostic tests. Overall, the studies demonstrated alterations in amino acid metabolism and several aspects of lipid metabolism including circulating fatty acids, triglycerides, phospholipids and bile acids. Although we report several studies that identified potential biomarkers, few have been validated.

Novel Knowledge-Based Transcriptomic Profiling of Lipid Lysophosphatidylinositol-Induced Endothelial Cell Activation

To determine whether pro-inflammatory lipid lysophosphatidylinositols (LPIs) upregulate the expressions of membrane proteins for adhesion/signaling and secretory proteins in human aortic endothelial cell (HAEC) activation, we developed an EC biology knowledge-based transcriptomic formula to profile RNA-Seq data panoramically. We made the following primary findings: first, G protein-coupled receptor 55 (GPR55), the LPI receptor, is expressed in the endothelium of both human and mouse aortas, and is significantly upregulated in hyperlipidemia; second, LPIs upregulate 43 clusters of differentiation (CD) in HAECs, promoting EC activation, innate immune trans-differentiation, and immune/inflammatory responses; 72.1% of LPI-upregulated CDs are not induced in influenza virus-, MERS-CoV virus- and herpes virus-infected human endothelial cells, which hinted the specificity of LPIs in HAEC activation; third, LPIs upregulate six types of 640 secretomic genes (SGs), namely, 216 canonical SGs, 60 caspase-1-gasdermin D (GSDMD) SGs, 117 caspase-4/11-GSDMD SGs, 40 exosome SGs, 179 Human Protein Atlas (HPA)-cytokines, and 28 HPA-chemokines, which make HAECs a large secretory organ for inflammation/immune responses and other functions; fourth, LPIs activate transcriptomic remodeling by upregulating 172 transcription factors (TFs), namely, pro-inflammatory factors NR4A3, FOS, KLF3, and HIF1A; fifth, LPIs upregulate 152 nuclear DNA-encoded mitochondrial (mitoCarta) genes, which alter mitochondrial mechanisms and functions, such as mitochondrial organization, respiration, translation, and transport; sixth, LPIs activate reactive oxygen species (ROS) mechanism by upregulating 18 ROS regulators; finally, utilizing the Cytoscape software, we found that three mechanisms, namely, LPI-upregulated TFs, mitoCarta genes, and ROS regulators, are integrated to promote HAEC activation. Our results provide novel insights into aortic EC activation, formulate an EC biology knowledge-based transcriptomic profile strategy, and identify new targets for the development of therapeutics for cardiovascular diseases, inflammatory conditions, immune diseases, organ transplantation, aging, and cancers.

Genetics Is of the Essence to Face NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the commonest cause of chronic liver disease worldwide. It is closely related to obesity, insulin resistance (IR) and dyslipidemia so much so it is considered the hepatic manifestation of the Metabolic Syndrome. The NAFLD spectrum extends from simple steatosis to nonalcoholic steatohepatitis (NASH), a clinical condition which may progress up to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). NAFLD is a complex disease whose pathogenesis is shaped by both environmental and genetic factors. In the last two decades, several heritable modifications in genes influencing hepatic lipid remodeling, and mitochondrial oxidative status have been emerged as predictors of progressive hepatic damage. Among them, the patatin-like phospholipase domain-containing 3 (PNPLA3) p.I148M, the Transmembrane 6 superfamily member 2 (TM6SF2) p.E167K and the rs641738 membrane bound-o-acyltransferase domain-containing 7 (MBOAT7) polymorphisms are considered the most robust modifiers of NAFLD. However, a forefront frontier in the study of NAFLD heritability is to postulate score-based strategy, building polygenic risk scores (PRS), which aggregate the most relevant genetic determinants of NAFLD and biochemical parameters, with the purpose to foresee patients with greater risk of severe NAFLD, guaranteeing the most highly predictive value, the best diagnostic accuracy and the more precise individualized therapy.

Mitochondria Matter: Systemic Aspects of Nonalcoholic Fatty Liver Disease (NAFLD) and Diagnostic Assessment of Liver Function by Stable Isotope Dynamic Breath Tests

The liver plays a key role in systemic metabolic processes, which include detoxification, synthesis, storage, and export of carbohydrates, lipids, and proteins. The raising trends of obesity and metabolic disorders worldwide is often associated with the nonalcoholic fatty liver disease (NAFLD), which has become the most frequent type of chronic liver disorder with risk of progression to cirrhosis and hepatocellular carcinoma. Liver mitochondria play a key role in degrading the pathways of carbohydrates, proteins, lipids, and xenobiotics, and to provide energy for the body cells. The morphological and functional integrity of mitochondria guarantee the proper functioning of β-oxidation of free fatty acids and of the tricarboxylic acid cycle. Evaluation of the liver in clinical medicine needs to be accurate in NAFLD patients and includes history, physical exam, imaging, and laboratory assays. Evaluation of mitochondrial function in chronic liver disease and NAFLD is now possible by novel diagnostic tools. "Dynamic" liver function tests include the breath test (BT) based on the use of substrates marked with the non-radioactive, naturally occurring stable isotope 13C. Hepatocellular metabolization of the substrate will generate 13CO2, which is excreted in breath and measured by mass spectrometry or infrared spectroscopy. Breath levels of 13CO2 are biomarkers of specific metabolic processes occurring in the hepatocyte cytosol, microsomes, and mitochondria. 13C-BTs explore distinct chronic liver diseases including simple liver steatosis, non-alcoholic steatohepatitis, liver fibrosis, cirrhosis, hepatocellular carcinoma, drug, and alcohol effects. In NAFLD, 13C-BT use substrates such as α-ketoisocaproic acid, methionine, and octanoic acid to assess mitochondrial oxidation capacity which can be impaired at an early stage of disease. 13C-BTs represent an indirect, cost-effective, and easy method to evaluate dynamic liver function. Further applications are expected in clinical medicine. In this review, we discuss the involvement of liver mitochondria in the progression of NAFLD, together with the role of 13C-BT in assessing mitochondrial function and its potential use in the prevention and management of NAFLD.

Lysophosphatidylinositol, especially albumin-bound form, induces inflammatory cytokines in macrophages

Lysophosphatidylinositol (LPI) is a glycero-lysophospholipid and a natural agonist against GPR55. The roles of the LPI/GPR55 axis in the pathogenesis of inflammation have been controversial. In the present study, we attempted to elucidate the roles of the LPI/GPR55 axis in inflammation, especially the secretion of inflammatory cytokines, IL-6 and TNF-α from macrophages. We treated RAW264.7 cells and mouse peritoneal macrophages (MPMs) with LPI and observed that LPI induced the secretion of IL-6 and TNF-α from these cells, as well as the phosphorylation of p38. These responses were inhibited by treatment with CID16020046 (CID), an antagonist against GPR55, or SB202190, an inhibitor of p38 cascade or knockdown of GPR55 with siRNA. Treatment with CID or ML-193, another antagonist against GPR55, attenuated the elevation of inflammatory cytokines in the plasma or tissue of db/db mice and in a septic mouse model induced using lipopolysaccharide, suggesting contributions to the improvement of insulin resistance and protection against organ injuries by treatment with CID or ML-193, respectively. In human subjects, although the serum LPI levels were not different, the levels of LPI in the lipoprotein fractions were lower and the levels in the lipoprotein-depleted fractions were higher in subjects with diabetes. LPI bound to albumin induced the secretion of IL-6 and TNF-α from RAW264.7 cells to a greater degree than LPI bound to LDL or HDL. These results suggest that LPI, especially the albumin-bound form, induced inflammatory cytokines depending on the GPR55/p38 pathway, which might contribute to the pathogenesis of obesity-induced inflammation and acute inflammation.

Relaxin has beneficial effects on liver lipidome and metabolic enzymes

Relaxin is an insulin-like hormone with pleiotropic protective effects in several organs, including the liver. We aimed to characterize its role in the control of hepatic metabolism in healthy rats. Sprague-Dawley rats were treated with human recombinant relaxin-2 for 2 weeks. The hepatic metabolic profile was analyzed using UHPLC-MS platforms. Hepatic gene expression of key enzymes of desaturation (Fads1/Fads2) of n-6 and n-3 polyunsaturated fatty acids (PUFAs), of phosphatidylethanolamine (PE) N-methyltransferase (Pemt), of fatty acid translocase Cd36, and of glucose-6-phosphate isomerase (Gpi) were quantified by Real Time-PCR. Activation of 5'AMP-activated protein kinase (AMPK) was analyzed by Western Blot. Relaxin-2 significantly modified the hepatic levels of 19 glycerophospholipids, 2 saturated (SFA) and 1 monounsaturated (MUFA) fatty acids (FA), 3 diglycerides, 1 sphingomyelin, 2 aminoacids, 5 nucleosides, 2 nucleotides, 1 carboxylic acid, 1 redox electron carrier, and 1 vitamin. The most noteworthy changes corresponded to the substantially decreased lysoglycerophospholipids, and to the clearly increased FA (16:1n-7/16:0) and MUFA + PUFA/SFA ratios, suggesting enhanced desaturase activity. Hepatic gene expression of Fads1, Fads2, and Pemt, which mediates lipid balance and liver health, was increased by relaxin-2, while mRNA levels of the main regulator of hepatic FA uptake Cd36, and of the essential glycolysis enzyme Gpi, were decreased. Relaxin-2 augmented the hepatic activation of the hepatoprotector and master regulator of energy homeostasis AMPK. Relaxin-2 treatment also rised FADS1, FADS2, and PEMT gene expression in cultured Hep G2 cells. Our results bring to light the hepatic metabolic features stimulated by relaxin, a promising hepatoprotective molecule.

Interactions between lysophosphatidylinositol receptor GPR55 and sphingosine-1-phosphate receptor S1P5 in live cells

Lysophosphatidylinositol (LPI) and sphingosine-1-phosphate (S1P) are bioactive lipids implicated in various cellular events including proliferation, migration, and cancer progression. LPI and S1P act as ligands for G-protein coupled GPR55 and S1P receptors, respectively, and activate specific signaling pathways. Both receptors are highly expressed in various cancer tissues and associated with tumor progression. However, physical and functional crosstalk between the two receptors has not been elucidated to date. Bioluminescence resonance energy transfer (BRET) experiments in the current study showed that S1P₅ strongly and specifically interacts with GPR55. We observed co-internalization of both receptors upon agonist stimulation. Notably, activation of one receptor induced co-internalization of the partner receptor. Next, we examined functional crosstalk of the two receptors. Interestingly, while activation of the individual receptors augmented cell proliferation, ERK phosphorylation and cancer-associated gene expression in HCT116 cells, co-activation of both receptors inhibited these stimulatory effects. Our collective findings indicate that GPR55 and S1P₅ form a heterodimer and their co-activation attenuates the stimulatory activity of each receptor on colon cancer progression.

Metabolic Landscape of the Mouse Liver by Quantitative 31 P Nuclear Magnetic Resonance Analysis of the Phosphorome

BACKGROUND AND AIMS

The liver plays a central role in all metabolic processes in the body. However, precise characterization of liver metabolism is often obscured by its inherent complexity. Phosphorylated metabolites occupy a prominent position in all anabolic and catabolic pathways. Here, we develop a ³¹ P nuclear magnetic resonance (NMR)-based method to study the liver "phosphorome" through the simultaneous identification and quantification of multiple hydrophilic and hydrophobic phosphorylated metabolites.

APPROACH AND RESULTS

We applied this technique to define the metabolic landscape in livers from a mouse model of the rare disease disorder congenital erythropoietic porphyria (CEP) as well as two well-known murine models of nonalcoholic steatohepatitis: one genetic, methionine adenosyltransferase 1A knockout mice, and the other dietary, mice fed a high-fat choline-deficient diet. We report alterations in the concentrations of phosphorylated metabolites that are readouts of the balance between glycolysis, gluconeogenesis, the pentose phosphate pathway, the tricarboxylic acid cycle, and oxidative phosphorylation and of phospholipid metabolism and apoptosis. Moreover, these changes correlate with the main histological features: steatosis, apoptosis, iron deposits, and fibrosis. Strikingly, treatment with the repurposed drug ciclopirox improves the phosphoromic profile of CEP mice, an effect that was mirrored by the normalization of liver histology.

CONCLUSIONS

In conclusion, these findings indicate that NMR-based phosphoromics may be used to unravel metabolic phenotypes of liver injury and to identify the mechanism of drug action.

Mechanisms and disease consequences of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide. Its more advanced subtype, nonalcoholic steatohepatitis (NASH), connotes progressive liver injury that can lead to cirrhosis and hepatocellular carcinoma. Here we provide an in-depth discussion of the underlying pathogenetic mechanisms that lead to progressive liver injury, including the metabolic origins of NAFLD, the effect of NAFLD on hepatic glucose and lipid metabolism, bile acid toxicity, macrophage dysfunction, and hepatic stellate cell activation, and consider the role of genetic, epigenetic, and environmental factors that promote fibrosis progression and risk of hepatocellular carcinoma in NASH.

Genetic predisposition similarities between NASH and ASH: Identification of new therapeutic targets

Fatty liver disease can be triggered by a combination of excess alcohol, dysmetabolism and other environmental cues, which can lead to steatohepatitis and can evolve to acute/chronic liver failure and hepatocellular carcinoma, especially in the presence of shared inherited determinants. The recent identification of the genetic causes of steatohepatitis is revealing new avenues for more effective risk stratification. Discovery of the mechanisms underpinning the detrimental effect of causal mutations has led to some breakthroughs in the comprehension of the pathophysiology of steatohepatitis. Thanks to this approach, hepatocellular fat accumulation, altered lipid droplet remodelling and lipotoxicity have now taken centre stage, while the role of adiposity and gut-liver axis alterations have been independently validated. This process could ignite a virtuous research cycle that, starting from human genomics, through omics approaches, molecular genetics and disease models, may lead to the development of new therapeutics targeted to patients at higher risk. Herein, we also review how this knowledge has been applied to: a) the study of the main PNPLA3 I148M risk variant, up to the stage of the first in-human therapeutic trials; b) highlight a role of MBOAT7 downregulation and lysophosphatidyl-inositol in steatohepatitis; c) identify IL-32 as a candidate mediator linking lipotoxicity to inflammation and liver disease. Although this precision medicine drug discovery pipeline is mainly being applied to non-alcoholic steatohepatitis, there is hope that successful products could be repurposed to treat alcohol-related liver disease as well.

GPCRs get fatty: the role of G protein-coupled receptor signaling in the development and progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), characterized by the abnormal deposition of lipids within the liver not due to alcohol consumption, is a growing epidemic affecting over 30% of the United States population. Both simple fatty liver and its more severe counterpart, nonalcoholic steatohepatitis, represent one of the most common forms of liver disease. Recently, several G protein-coupled receptors have emerged as targets for therapeutic intervention for these disorders. These include those with known hepatic function as well as those involved in global metabolic regulation. In this review, we highlight these emerging therapeutic targets, focusing on several common themes including their activation by microbial metabolites, stimulatory effect on insulin and incretin secretion, and contribution to glucose tolerance. The overlap in ligands, localization, and downstream effects of activation indicate the interdependent nature of these receptors and highlight the importance of this signaling family in the development and prevention of NAFLD.

Role of G Protein-Coupled Receptors in Hepatic Stellate Cells and Approaches to Anti-Fibrotic Treatment of Non-Alcoholic Fatty Liver Disease

The prevalence of non-alcoholic fatty liver disease (NAFLD) is globally increasing. Gaining control over disease-related events in non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, is currently an unmet medical need. Hepatic fibrosis is a critical prognostic factor in NAFLD/NASH. Therefore, a better understanding of the pathophysiology of hepatic fibrosis and the development of related therapies are of great importance. G protein-coupled receptors (GPCRs) are cell surface receptors that mediate the function of a great variety of extracellular ligands. GPCRs represent major drug targets, as indicated by the fact that about 40% of all drugs currently used in clinical practice mediate their therapeutic effects by acting on GPCRs. Like many other organs, various GPCRs play a role in regulating liver function. It is predicted that more than 50 GPCRs are expressed in the liver. However, our knowledge of how GPCRs regulate liver metabolism and fibrosis in the different cell types of the liver is very limited. In particular, a better understanding of the role of GPCRs in hepatic stellate cells (HSCs), the primary cells that regulate liver fibrosis, may lead to the development of drugs that can improve hepatic fibrosis in NAFLD/NASH. In this review, we describe the functions of multiple GPCRs expressed in HSCs, their roles in liver fibrogenesis, and finally speculate on the development of novel treatments for NAFLD/NASH.

Cannabinoid receptor type 1 antagonist inhibits progression of obesity-associated nonalcoholic steatohepatitis in a mouse model by remodulating immune system disturbances

SCOPE

This study investigated whether AM251, a cannabinoid receptor type 1 (CB1) antagonist, ameliorates hepatic levels of metabolic abnormalities and inflammatory responses in a murine nonalcoholic steatohepatitis (NASH) model via reversal of disturbances in the immune system.

METHODS AND RESULTS

Fifteen-week-old male obese db/db mice were randomly assigned to the following two groups: no treatment and treatment with AM251 at 5 mg/kg for 15 days. C57BL/6J-Lean mice were utilized as the control group. Plasma parameters, liver histopathology, and hepatic status were measured. For the in vitro study, macrophage-derived RAW264.7 cells were cultured with AM251 or CB1 small interfering RNA (siRNA) before challenge with arachidonyl-2'-chloroethylamide (ACEA) or a high concentration of fatty acids (HFFAs). The db/db mice exhibited an increase in CB1 levels, lipid droplet accumulation, mitogen-activated protein kinase-related inflammatory responses, and macrophage and neutrophil infiltration in the liver tissues. Flow cytometry analysis revealed an elevation in macrophages and T helper cells, plus a decrease in natural killer T cells and regulatory T cells in the liver tissues of the db/db mice; treatment with 5 mg/kg AM251 reversed these changes. Moreover, in vitro experiments revealed that administration of 3.3 μM AM251 or CB1 siRNA prevented 1 mM HFFA- and 1 μΜ ACEA-induced inflammatory cytokine protein expression in the RAW264.7 cells.

CONCLUSION

These findings suggested that a blockade caused by CB1 reduced obesity-associated NASH progression via correction of immune system dysregulations and elevated inflammatory responses in the liver tissues.

Imbalance of Endocannabinoid/Lysophosphatidylinositol Receptors Marks the Severity of Alzheimer's Disease in a Preclinical Model: A Therapeutic Opportunity

Alzheimer's disease (AD) is the most common form of neurodegeneration and dementia. The endocannabinoid (ECB) system has been proposed as a novel therapeutic target to treat AD. The present study explores the expression of the ECB system, the ECB-related receptor GPR55, and cognitive functions (novel object recognition; NOR) in the 5xFAD (FAD: family Alzheimer's disease) transgenic mouse model of AD. Experiments were performed on heterozygous (HTZ) and homozygous (HZ) 11 month old mice. Protein expression of ECB system components, neuroinflammation markers, and β-amyloid (Aβ) plaques were analyzed in the hippocampus. According to the NOR test, anxiety-like behavior and memory were altered in both HTZ and HZ 5xFAD mice. Furthermore, both animal groups displayed a reduction of cannabinoid (CB1) receptor expression in the hippocampus, which is related to memory dysfunction. This finding was associated with indirect markers of enhanced ECB production, resulting from the combination of impaired monoacylglycerol lipase (MAGL) degradation and increased diacylglycerol lipase (DAGL) levels, an effect observed in the HZ group. Regarding neuroinflammation, we observed increased levels of CB2 receptors in the HZ group that positively correlate with Aβ's accumulation. Moreover, HZ 5xFAD mice also exhibited increased expression of the GPR55 receptor. These results highlight the importance of the ECB signaling for the AD pathogenesis development beyond Aβ deposition.

MBOAT7 down-regulation by genetic and environmental factors predisposes to MAFLD

Metabolic associated fatty liver disease (MAFLD) encompasses a broad spectrum of hepatic disorders, which include steatosis, nonalcoholic steatohepatitis (NASH), fibrosis and cirrhosis, that is a critical risk factor for hepatocellular carcinoma (HCC) development. Its pathogenesis is intertwined with obesity and type 2 diabetes (T2D). However, the predisposition to develop MAFLD is severely influenced by environmental and inherited cues. The rs641738 variant close to MBOAT7 gene has been identified by a genome-wide association screening in heavy drinkers. Although this variant has been associated with the entire spectrum of MAFLD, these results have not been completely replicated and the debate is still opened. Thus, functional studies that unravel the biological mechanisms underlying the genetic association with fatty liver are required. This review aims to summarize the clinical and experimental findings regarding the rs641738 variation and MBOAT7 function, with the purpose to shed light to its role as novel player in MAFLD pathophysiology.